1. Field of the Invention.
This invention relates to skis and snow skiing, and more particularly to a method and apparatus that enables a skier to achieve enhanced maneuverability and improved speed control in the activity of downhill snow skiing.
2. Description of the Prior Art.
A review of the prior art has convinced me that the subject of the instant invention is the only method and apparatus which:
(a) provides a downhill skier with enhanced control over both axial drag and lateral maneuverability; and PA1 (b) provides both of the above enhancements by selective use of the skier's natural body movements.
A search of the prior art has revealed the existence of the following U.S. Pat. Nos.
______________________________________ 3,980,322 3,918,730 3,909,024 3,195,911 3,048,418 4,152,007 4,103,916 4,062,561 4,227,708 3,873,108 4,312,517 4,227,714 ______________________________________
At the outset, it is well to understand that the invention forming the subject matter of this specification does not concern the problem of stopping a loose ski that has become separated from a skier. Rather, this invention focuses on the problem of imposing additional controlling forces on the skis in a downhill skiing environment in such a way that the skier will feel more in control at the speed at which he is descending.
Referring to the patents listed above, all of the patents except U.S. Pat. Nos. 4,152,007 and 4,227,708 relate to the situation where a ski has been separated from a skier and is loose on the ski slope and apt to cause some damage or injury to skiers unless stopped. These "loose ski brake" devices do not operate during active skiing, and are clearly unrelated to the structure and function of the invention described herein.
U.S. Pat. No. 4,152,007 provides snow plows at the rear ends of the skis that are activated by hydraulic pressure controlled through the grips on the ski poles. Obviously, there must be some connection between the grips on the ski poles and the snow plows and this in itself is a disadvantage in that the skier is prevented from utilizing the ski poles as freely as he might for the purpose for which they are intended. This device provides active drag control, which is the only function it shares with my invention described herein. The characteristics of this device are in sharp contrast with the enhanced maneuverability provided by my invention. Because the plows in this device are at the rear ends of the skis and therefore far behind the skier's center of gravity, they actually tend to prevent the skier from turning while they are engaged. The hydraulic actuation is also significantly different than the normal skiing motions that are effective to control the maneuverability characteristics of my invention. Therefore, this device is clearly functionally and structurally different from my method and apparatus.
U.S. Pat. No. 4,227,708 relates to a ski brake that comprises a plate fixed on the upper surface of the ski. The plate is provided with a notch into which the lower end of the ski pole may be inserted to produce drag against the snow. While the primary purpose of this device is to provide traction in cross-country skiing, it purports to provide active braking for a cross-country skier moving downhill. Active braking is also one of the at least three important functions of my apparatus. However, this device does not provide either the enhanced maneuverability or control by natural body motions provided by my apparatus. Maneuverability is an essential difference between downhill skiing and cross-country skiing. The bindings of cross-country skis naturally limit maneuverability. Since this device applies drag only on the outside of the skis, downhill braking would tend to spread the tips of the skis, making the skis even more difficult to maneuver. Use of the ski poles as braking levers violates the natural motions of downhill skiing which requires upper body movement and free use of the poles. Therefore, this device, while obviously structurally different from my apparatus in all its embodiments, is also clearly incapable of performing two of at least three major functions performed by my apparatus.
For those that are experienced skiers, it will be obvious that skiing on a steep slope requires considerably more physical effort and skill than skiing on a gentle slope. Turning maneuvers to reduce speed require the skier to generate a force in opposition to the force tending to propel the skier downhill. This force, multiplied by the skier's velocity, equates with the power the skier must exert to maintain speed control on the slope. Steeper slopes require both a greater maximum force and a greater average power which together require greater strength and endurance from the skier. Expert skiers have several advantages over less advanced skiers. First, since they have a higher ability threshold, a greater fraction of the potential energy during the run is consumed in aerodynamic and ski drag. Second, since they are more skillful, they are able to make turns with less muscle strain. Although expert skiers still must exert the same force as less experienced skiers, they apply it more effectively in reducing speed.
As stated above, the primary purpose of my method and apparatus is to enhance the safe enjoyment of downhill skiing by significantly reducing the level of skill and physical strength required to participate in the sport.
The method and apparatus of my invention enables a skier to safely handle terrain that would otherwise be beyond his ability. It is believed that wide spread use of my method and apparatus will increase the number of individuals participating in downhill skiing and will reduce the number of injuries sustained by such participants when they are inadvertently caught in situations beyond their ability.
The sport of downhill skiing involves executing trained physical body motions that change the skier's spacial orientation and weight distribution as the skis slide across the snow. The maneuvers that result from such body motions enable the skier to control his direction and most importantly his speed.
In the sport of downhill skiing, the skier converts potential energy into mechanical work and ultimately into heat. By the conservation of energy, the rate of change of potential energy equals the rate of change of kinetic energy plus the rate of mechanical work performed by the skier. This mechanical work rate (or power) is the skier's velocity times the snow friction and air drag. Steeper slopes require a greater friction plus drag force to hold a given speed than more gentle slopes.
A skier's strength and skiing ability determine the steepness of the slope that he can comfortably and safely handle. Skiing skill determines how efficiently a skier can convert muscle force into useful drag. The snow-plow is a perfect example of an inefficient skiing maneuver. In the snow-plow the skier pushes outward on his skis and thereby creates an axial force equal to his lateral force times the sine of the angle of his skis. Since the "V" half angle of his skis is typically only about 15 degrees or less only one quarter of his lateral force is converted into useful drag. This situation is compounded by the awkward nature of the snow-plow maneuver.
Proficient skiers have several advantages over beginning skiers. First, they can ski at a higher average speed letting ski friction and aerodynamic drag (which are relatively non-fatiguing) generate mechanical work at a faster rate. Second, they can convert muscle force more efficiently into useful drag. A good parallel skier can seemingly effortlessly make small turns and efficiently use his leg muscles to react the drag force needed to keep his speed under control. Third, the proficient skier is often in better physical condition and has greater strength and endurance than beginning skiers.
Enjoyable skiing is a process of speed control. If a skier is not in excellent condition, and he is unable to efficiently convert his muscle forces into drag, he will either be limited to gentle and uninteresting terrain or, more typically, he will ski on terrain beyond his ability and risk injury to himself and others. Unfortunately, our modern society neither encourages physical fitness nor provides extended leisure time to learn new activities. This results in millions of people who would like to enjoy downhill skiing, but have not found the time to become advanced intermediate skiers where they can really begin to enjoy the sport. Accordingly, a method and apparatus such as described herein is needed to reduce the level of skill required to enjoy downhill skiing by permitting skiers to more efficiently convert muscle force into speed control and maneuverability while retaining the natural motions of skiing.
Another element enters into the method of speed control and has been alluded to somewhat above. That is the fact that conventionally speed control is effected by manipulating turns on the slope to introduce a force that is in opposition to the downhill acceleration force that is imposed by gravity and the steepness of the slope. Accordingly, if some method or means could be devised by which turns could be effected without the imposition of discomfort on the skier or the utilization of excessive muscle force, then the skier would be more likely to attempt a run on a steep slope that he would not otherwise feel comfortable with.
Accordingly, one of the important objects of the present invention is to provide a method and means by which a skier may selectively control maneuverability and therefore speed on a downhill ski slope.
The invention achieves selective maneuverability and speed control by adding fluid dynamic control surfaces on downhill skis to enhance both axial drag and maneuverability using a skier's natural motions. These additional control surfaces generate forces that augment the edge control forces on the skis. The control surfaces of my invention, referred to herein as "probes", are analogous to the spoiler/flap system on modern jet airplanes in terms of vehicle drag and stability characteristics. Since snow only produces loads below the running surface of the ski, another object of my invention is the provision of a method and apparatus for differentially varying probe depth on the inside and outside edges of the skis.
The following discussion illustrates how the probes of my invention enhance the speed and maneuverability control characteristics of snow skis. The detailed description of the structures (including the probes) that provide these characteristics is presented later in this disclosure. That description also presents features of the structures which facilitate the operation of the invention but which do not directly affect the speed and maneuverability control aspects discussed below.
Accordingly, a still further object of the invention is the provision of apparatus which in the engaged or operative position, extends two probes on each ski a precise distance below the running surface of the ski into the snow. These probes act as additional control surfaces that augment the forces acting on the other ski surfaces during downhill skiing.
A still further object of the invention is the provision of apparatus in conjunction with snow skis which when engaged and operative, has the effect of making a slope appear to be more gentle, and which includes probes which project below the running surface of the ski to provide additional drag which reduces the skier's acceleration and terminal velocity.
Still another object of the invention is the provision of apparatus for snow skis, including projecting probes, which can be adjusted either before or during a run so as to adjust the basic drag coefficient by adjusting the depth of the probe's extension below the running surface of the skis.
Although these steady drag effects are important, the primary additive drag effects occur as a result of skier controlled probe depth variation during the ski run. Tests have shown that the drag imposed on a ski by a probe projecting into the snow is a strong function of probe depth. Accordingly, a still further object of the invention is the provision of an apparatus including pairs of probes attached to the skis in such a manner that rotating the ski about the longitudinal axis increases the penetration depth on one probe and decreases the penetration depth of the other probe on that ski. This differential probe depth causes a significant increase in the total drag, because of the large increase in drag on the deeper probe. This has two primary applications in downhill skiing speed control as will now be explained. The snow-plow maneuver becomes far more effective and less strenuous to execute. Simply rotating the knees together (with the skis pointed straight) produces a large drag increase due to the greater penetration of the inside probes. The differential torque created by the drag on the inside probes automatically draws the ski tips together, adding the normal snow-plow edge drag, but without the muscle strain normally required. Rotating the knees back to vertical returns the skis to normal parallel position and equalizes the forces on the skis, cancelling the differential torque.
Parallel turns are more effective in achieving speed reduction when the skis are equipped with my probe system. The edge drag is supplemented by probe drag. Effective speed control can be accomplished with very little edge drag which is quite helpful under poor snow conditions.
Turning ability, which is a major factor in maneuverability, is significantly enhanced because the probes enable turning by leaning. For example, leaning to the right increases the penetration depth and drag on the right probes on both skis and decreases the depth and drag on the left probes. This both increases the total drag and creates a rotational moment that turns the skis to the right. Similarly, leaning to the left turns the skier to the left. As discussed below, the skier can further enhance turning ability by leaning slightly backward as he leans to the left or right.
The method and apparatus of my invention provides "trim" adjustment to reduce muscle strain associated with holding the skis together. Most people walk with their feet slightly spread apart and their muscles are adjusted to that position. Therefore, parallel skiing requires a constant muscle strain to hold the tips of the skis together. With my method and apparatus, a skier can alleviate this condition by adjusting the depth of penetration of the inside probes to be slightly greater than the depth of penetration of the outside probes. This creates a toe-in moment on the skis which keeps the tips together without continuous muscle strain by the skier.
The following discussion relates to the features of my invention which, taken individually or in combination, account for the speed control and maneuverability enhancement characteristics discussed above.
1. Precise depth control. -- Since drag is a strong function of depth, the probes of my invention are designed to provide precise setting and control of their extension past the running surface of the skis.
2. Probe center of pressure location. -- Probe location near the center of pressure of the skis, which is also near the skier's center of gravity when sking downhill is necessary to provide the desired neutral lateral stability characteristics. Locating the probes aft of the skier's center of gravity (i.e., a positive stability margin as in the classic loose ski brake) would make turning more difficult because the probes would produce a restoring moment tending to keep the skis pointed in the direction of travel. Locating the probes forward of the center of gravity (i.e. negative stability margin) would make the skis rotationally unstable.
The foregoing will be better understood if it is considered that many skis are visually marked with a center of gravity indicia located about midway between the toe piece and the heel piece. However, this location of the indicia marks the center of gravity of the ski and skier when the skier is standing erect or vertically, or "at rest" on the skis. In a downhill run, the skier leans forward, his body mass also moves forward in relation to the skis, and so does the center of gravity, which is now located forwardly from the indicia and at the intersection of the vertical projection of the skier's body mass and the plane of the skis. This forward position of the center of gravity of the skier is correlated to the probe location associated with the center of pressure of the skis, which I have found to be closely associated with the toe piece.
Accordingly, my invention locates the probes about the middle of the toe piece of the ski boot attachment means which is the natural location of the center of pressure and the skier's center of gravity when the skier is leaning slightly forward in a downhill run. Obviously, the exact optimum location will vary somewhat depending on the skier and the terrain. The skier can control his center of gravity location in relation to probe location associated with the center of pressure and thereby control the stability characteristics of his skis. By leaning forward (and moving his center of gravity forward of the probes) the probes act to keep the skis pointed in the direction of travel and stabilize any lateral oscillations. By leaning backward during turning, the skier can enhance turning by moving the center of gravity slightly aft of the probes and making the skis deliberately unstable. The skier would obviously do this after he had started a turn and had both his skis clearly rotated in one direction.
3. Two pin characteristics.--Many of the desirable characteristics of my method and apparatus require two pins (one on each side of the ski). A single pin configuration as illustrated in FIGS. 14 and 15, locates the pin under the toe piece and provides a steady drag and facilitates turning by the center of gravity shift mechanism discussed above. However, the two pin design adds the ability to increase drag by leaning as in parallel turns or by rotating the knees together, as in a snow-plow maneuver. The turning by leaning feature requires a two pin arrangement; the turning by aft center of gravity shift only starts to work after the skis have rotated relative to the direction of travel.
4. Probe lift-drag characteristics.--The shape and orientation of the probes are important in establishing the operating characteristics of the method and apparatus of my invention. While I have illustrated and described herein probes which constitute cylindrical rods, it is apparent that other configurations may be utilized within the spirit and scope of the invention. As indicated above, the preferred probe configurations shown in the embodiment illustrated are all cylindrical. This axisymmetric shape is an advantage because it provides the facility to provide for the threaded depth adjustments used on several of the embodiments. However, the probes are not restricted to axisymmetric shapes. Shapes such as ellipsis, wedges, airfoils or other profiles offer potential advantages under certain conditions and are intended to be covered within the scope of this invention.
With respect to orientation of the pins, vertical pins produce no lift, and this is an advantage for the beginning skier. Rotating the skis to produce drag does not require any force to overcome lift. This is an advantage for the snow-plow maneuver, but less important for the turning by leaning maneuver. Vertical pins provide higher drag (and slower speeds) under poor snow conditions.
As illustrated in the drawings, and described hereinafter, a slightly backwards probe cant is the preferred orientation for the probes. The cant reduces the drag coefficient parallel to the skis without significantly changing the drag coefficient perpendicular to the skis. These characteristics mean less steady state drag with the same turning ability due to the high drag perpendicular to the skis. The lift produced on icy snow reduces the penetration depth and reduces the drag parallel to the skis without affecting turning ability. Again, the optimum cant angle depends on the skier, the terrain and snow conditions. Although the preferred embodiment incorporates canted probes, it will of course be obvious that the invention encompasses a full range of probe angles.
It appears that an unexpected benefit is derived by the use of my method and apparatus that relates to the condition of a ski slope. Conventionally, ski slopes are used during daylight hours and are "groomed" during the night time to prepare them for another full day of skiing the following day. I have found that because the control forces applied to the skis by the probes are relatively small and because packed snow is a viscous fluid, probe depth of only 1/4 to 1/2 inch appear to be adequate for most conditions. I have found that penetration of the snow by the probes creates a hardly perceptible groove in the snow. Tests have shown that the almost imperceptible grooves left by the probes are almost invisible and quickly disappear in normal pack-powder snow. I have also found that these tiny grooves appear to help groom the slopes under high packed or moderately icy snow conditions. When the snow becomes icy, edge control becomes difficult because the edge loading is insufficient to cause penetration of the snow by the ski edge. This is also true for the probes under severely icy conditions. However, under hard packed or moderately icy conditions, the probes easily penetrate the snow surface. This feature gives the skiers significantly improved control under these conditions while the probes help break up the hard ice surface. Accordingly, if enough skiers use the probe system of my invention, it is easy to see that their combined actions would help prevent hard or icy layers from forming on the slopes.
The invention possesses other objects and features of advantage, some of which with the foregoing will be apparent from the following description and the drawings. However, it is to be understood that the invention is not limited to the embodiments illustrated and described, since it may be embodied in various forms within the scope of the appended claims.